Paint adhesion for RIM parts

ABSTRACT

The addition of a small amount of a halogen compound, e.g. chloroethyl phosphate, in a process producing elastomeric polyurethane RIM parts using tertiary amines as the chief catalyst component results in scavenging the residual amines after the part has been cured by annealing. The parts from such a process can be coated with a wide variety of enamels having a high solids content and completely cured to result in a higher degree of adhesive between the coating and the part&#39;s surface than those parts from a process without the use of such a halogen.

TECHNICAL FIELD

The present invention relates to urethane formulations for use inproduction of products by reaction injection molding (RIM) and isparticularly concerned with improving the adhesion of resinous coatingsapplied to such products.

BACKGROUND OF THE INVENTION

Formulations for production of reaction injection molded elastomerpolyurethane products, such as those widely employed in the automotiveindustry, generally comprise a high molecular weight polyether polyoland an organic polyisocyanate together with volatile organic blowingagents and catalyts which may be tertiary amine, organo-tin compound, ormore generally a co-catalyst combination of tertiary amine and tincatalysts. Triethylene diamine catalyst, more often together with asmaller amount of tin co-catalyst, have been widely used in polyurethaneRIM formulations. In addition to the usual components common toformulations for blown polyurethane products, those employed in theformation of urethane elastomeric products by reaction injectionmolding, typically contain chain extenders, such as low molecular weightdiols (e.g. ethylene glycol or butane diol) and diamine (such as diethyltoluenediamine). The obtained RIM polymers contain the chemical bondformation of urethane, urea and to a lesser extent allophonate andbiuret, in which the polymer product comprises a build-up of hard andsoft block segments having the desired physical properties. Thissegmentation is controlled by the selection of reactants as well as bythe relative reaction rate between the polyol and isocyanate. The levelof catalysts and the type thereof has an important influence on thereaction rates.

To obtain good processability of a RIM part, the reactants should remainfluid in the initial stages for good flowability into the mold, but beviscous enough to prevent excess wetting of the mold surface and avoidair entrapment. While this can be achieved to greater or less extent bytin catalysts alone or by ditertiary amine catalyst such astriethylenediamine, alone, the combination of these has been foundbeneficial because of the remarkable synergism displayed.

When acrylic or melamine-based coatings of very high solids contentabove a particular level are applied to RIM products, it was found thatfrequently a tacky or soft finish was had. This was observedparticularly in those instances when the high solids coating was appliedto products produced from a RIM formulation containing a relativelylarge amount of tertiary amine catalyst. Since the acrylic and melaminebased coatings used are cured by acid, the resulting tacky finish wasattributed to the presence of residual amine in the molded polyurethaneproduct, which interfered with cross-linking reactions needed forcomplete cure of the coating polymer resin. In the case of RIMformulations containing less than 0.15 parts of triethylenediaminecatalyst per hundred parts of polymer (php), no adverse effects wereobserved on the surfaces coated with the very high solids enamels.Complete cures with no loss in physicals were obtained. Also, it wasfound that the incomplete curing of such higher solids coatings did notoccur when the RIM formulation comprised reactive hydroxyalkyl aminecatalysts (with less than 0.15 php of non-reactive tertiary amine). Inthat instance, as the elastomer is cured the reactive amine apparentlyis chemically bound to the urethane polymer backbone, preventing theamine from interfering with cure of the coating.

In investigations leading to the present invention numerous approacheswere considered and pursued to overcome the problem of incomplete cureof acid-catalyzed resin coatings of high solids content applied tomolded urethane products such as those produced by the RIM procedure. Itwas found that the problem presented could be overcome and acceptableacid-catalyzed resin coatings of high solids content could be obtainedon urethane surfaces containing volatile amines, by the inclusion ofcertain scavenger compounds in the RIM formulation.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided in the methodof producing elastomeric polyurethane molded products comprising thesteps of (a) injecting into a mold cavity a reactive mixture of a highmolecular weight polyetherpolyol, an organic polyisocyanate, an organicblowing agent and a catalyst composition for the reaction in which anon-reactive tertiary amine constitutes the major catalyst component ofthe reaction mixture; (b) removing the obtained polyurethane productfrom the mold, and (c) applying to the molded product an acid-catalyzedresin-base coating; the improvement which comprises enhancing completecuring of the coating by inclusion in the reaction mixture of an organichalogen compound in an amount providing the equivalent of about 1 to 1.5molar parts of reactive halogen per mole of available amino nitrogen inthe catalyst component of the mixture.

The principle of the invention is particularly applicable to urethaneformulations employed in making RIM products which are commonly given asurface coating with an acid-cured enamel of high solids content.

DETAILED DESCRIPTION OF THE INVENTION

Since only a small amount of the halogen compound is needed toaccomplish the stated objective, its inclusion in the urethaneformulation will not interfere with the production or quality of thedesired urethane products.

The halogen compound employed needs to be one capable of eventuallyreacting with residual amines, but only after the molded part has beencured. In other words, the rate of reaction of the halogen compound withthe amine should be substantially less than the rate of thepolymerization reaction taking place in formation of the urethane by thecatalyzed reaction of organic polyisocyanate and polyol.

Only a small amount of the halogen compound needs to be used forscavenging the residual amine as up to no more than about a molarequivalent of contained halogen in said compound per mole of aminonitrogen in the catalyst. Amounts of halogen in excess of about 3% byweight of polyol in the formulation may interfere with catalysis orotherwise impair the desired urethane reaction, unless compensatingchanges are made in the formulations conventionally employed.

Among the halogen compounds that may be employed for neutralizing theresidual amine, there are a number of compounds readily availablecommercially, including "Fryol CEF" (chloroethyl phosphate), "Thermolin101" (a chloroethyl phosphate dimer), chlorinated paraffins of highmolecular weight such as chlorinated paraffin wax (e.g. "Chlorowax 50")and chlorinated polyols (e.g. Olin's RF-230). Certain of these listedcompounds are employed as flame retardants; however, the amount thatneeds to be used in the urethane formulations of the present inventionis far below the level required to impart significant flame retardantproperties, their use above the level of about 3 parts by weight perhundred parts of polyol detract from the physical properties of theelastomers and thus such a level is undesirable as will be shown in theexamples below.

Typical RIM formulations are illustrated below:

                  TABLE 1                                                         ______________________________________                                                         A      B                                                     ______________________________________                                        .sup.(1) Pluracol® 380                                                                       80       100                                               .sup.(2) Multranol® 9151                                                                     20       --                                                1,4-butanediol     23       23                                                Fluorocarbon       4        4                                                 Catalyst                                                                      Triethylenediamine and                                                                           0.1-0.5  0.1-0.5                                           Tin, Dibutyl Tin diLaureate                                                                      0.02     0.02                                              or                                                                            Dibutyl Tin diLaurate alone                                                                      0.05-0.11                                                                              0.05-0.11                                         .sup.(3) Mondur® CD                                                                          79.5     79.5                                              ______________________________________                                         .sup.(1) High molecular weight (˜6500) polyether polyol supplied by     BASF Wyandotte.                                                               .sup.(2) Polyurea dispersion in polyether polyol supplied by Mobay            Chemical Co.                                                                  .sup.(3) Methylenediisocyanate containing carbodimide supplied by Mobay       Chemical Co.                                                             

In general, RIM formulations may contain per hundred parts highmolecular weight (above about 5000), polyol, 15 to 30 parts of butanediol or other low molecular weight diol, 0 to 4 parts of fluorocarbon orother organic blowing agent, and an amount of polyisocyanate providing 1to 1.05 molar equivalents of NCO per 1 equivalent of activehydrogen-containing compounds.

In the typical RIM procedure, the reactive urethane-producingcomposition, such as that shown in column A or B of Table 1 or a similarRIM formulation is injected into the mold cavity in which thepolyurethane product is formed. The product is removed from the mold andannealed. The surface is then washed with aqueous detergent, rinsed anddried to remove surface moisture. The top coat enamel is applied,generally over a previously applied dried primer coat, air dried and thecoated product is baked. Among other possible causes of incompletecuring of the top coat is the presence of amine at the surface of theurethane product which inhibits the effectiveness of the acid catalysisof the coating. Such amines may be present from urethane formulationswhich contain amino-based polyols or amino chain-extenders. Duringheating of the polyurethane product amino nitrogen may be caused toorient toward the surface. Also during curing by heating, volatile aminefrom the tertiary amine catalyst may rise to the surface and can reactwith the acid.

Products obtained by reaction injection molding using the formulationsof Table 1 or similar formulations have been successfully coated withacid-catalyzed enamels containing in the range of about 25% to about 35%solids (e.g. Durethane®300 Elastomeric Enamel). Also such RIM productscan be successfully coated with water-based enamels and with "color plusclear" coatings. As the solids content of acid-catalyzed, enamels areincreased, (e.g. in range of about 35 to about 42%) however, to reducethe number of required spray positions and solvent emissions, thesecoatings become more sensitive to environmental factors. This isparticularly evident with respect to obtaining complete curing of suchhigh solids coatings applied to RIM products prepared from formulationscontaining in excess of about 0.15 php of tertiary amine catalyst. Aswill be seen from the following examples, this problem of incompletecure is overcome when there is included in the RIM formulation areactable halogen compound in accordance with the invention.

The reaction between the residual amine in the RIM product and thehalogen compound is believed to result in tying up the amine, followingcatalysis of the urethane reaction, by the formation of a quaternaryamine. Thus, for example in the use of tris (chloroethyl phosphate), thereaction can be illustrated as ##STR1## After the quaternary aminehalide is formed the amine is no longer available to interfere with theacid in the coating.

EXAMPLE 1

Using the formulation 1A of Table 1 above, column A, urethane productswere prepared by injection molding in the conventional manner, employingthe amounts of catalyst indicated in Table 2, with and without addedhalogen compound as a scavenger. These products were each painted with aconventional melamine base automotive baked exterior enamel andsubjected to the listed tests, with the results indicated in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                          TEDA 0.5 php                                                                  CEF                                                                  TEDA T-12                                                                              .THorizBrace.                                                        0.5  00.9                                                                              5.0 2.5 1.0 TEDA 0.1 php                                PROCESS                                                                             TEST   php  php php php php DABCO®T 0.5 php                         __________________________________________________________________________    I     MEK    F    P   P   P   P   P                                           I     Humidity                                                                             P    P   P   P   P   P                                           I     Elongation %                                                                         199-285                                                                            52-65                                                                             43-55                                                                             49-55                                                                             53-69                                                                             65-83                                       II    MEK    F    P   P   P   P   P                                           II    Humidity                                                                             P    P   P   P   P   P                                           II    Elongation %                                                                         194-251                                                                            53-70                                                                             36-50                                                                             58-60                                                                             51-57                                                                             59-89                                       III   MEK    F    P   P   P   P   P                                           III   Humidity                                                                             P    P   P   P   P   P                                           III   Elongation %                                                                         214-233                                                                            54-83                                                                             50-57                                                                             46-52                                                                             65-76                                                                             59-74                                       __________________________________________________________________________     Process I-- Wash in aqueous solution comprising Ridoline 72 (Amchem) a        powdered, nonsilicated, alkaline detergent containing biodegradable           organic surfactants; followed by water rinse.                                 Process II-- Wash in mildly acidic detergent composition comprising           Ridoline 804 (Amchem); followed by water rinse.                               Process III-- Wash in 10% aqueous solution of P--toluene sulfonic acid        followed by water rinse.                                                      php = per hundred parts by weight of polyol                                   F = failed;                                                                   P = passed.                                                                   DABCO T is trimethylaminoethyl ethanolamine.                                  CEF is tris(chloroethyl) phosphate.                                           MEK is methyl ethyl ketone.                                              

Before subjecting the enamel coated RIM specimen part to the severaltests indicated in Table 2, the part was washed by each of the indicatedprocedures before being subjected to the tests.

In the standard MEK test, the part is rubbed lightly in a 1-inch circleabout 10 times with a cloth wet with MEK, then blow-dried. The driedsurface is scratched vigorously with the fingernail. If no film isthereby removed, the cure of the enamel is deemed sufficient and thetest is passed. If some film is removed, the cure is not sufficient andthe specimen has failed the test. In addition, for a mark of P (passed)the gloss on the surface should be unaffected after 1/2 hour air drying.

In the elongation test the enameled RIM specimen is cut into samplepieces, which are subjected to a pulling force at 2 inches per minute atroom temperature until the first crack appears in the paint film. Theattained % elongation is measured or calculated (by an incrementalextensometer) on the average of three samples tested.

The humidity test is run by subjecting the painted part to 96 hourexposure at 100% relative humidity at 37.7° C. followed by a two hourimmersion in hot water at 37.7° C. To pass the test there should be noevidence of blistering when examined one minute after removal from thetest cabinet.

From the test results set out in Table 2, it is apparent that RIM partsmade by polyurethane formulations employing tertiary amine catalyt inexcess of 0.15 parts per hundred parts of polyol did not pass thestandard tests designed to determine adhesion of paint to the surfacethereof. By the inclusion of a small amount of a halide scavengercompound in the formulation, the obtained RIM products had improvedpaint adhesion properties and were able to pass the standard tests. Informulations employing only tin catalyst without tertiary amine asco-catalyst, there was no problem of residual amine in the curedpolyurethane. Likewise, in the case in which reactive amine (such asDABCO-T) was employed together with a smaller amount of non-reactivetertiary amine catalyst in RIM formulations, the need for a halidescavenger in the formulation was obviated, provided that the amount ofnon-reactive catalyst (responsible for the unreacted amine residue) didnot exceed about 0.15 parts by weight per hundred parts of polyols inthe formulation. To be on the safe side, the scavenger use isrecommended when the non-reactive tertiary amine in the formulationexceeds about 0.1% by weight of polyols. By the inclusion of the halogenscavenger compounds in the formulation, a tertiary amine catalyst may beutilized in the formulation, if so desired, to levels of up to about 1.0php without adverse effect on applied acid-catalyzed high solidscoatings.

In practice of the present invention when employing tertiary aminecatalyst with or without a minor amount of organic tin co-catalyst, theorganic halogen scavenger compound should provide the equivalent ofabout 1 to 1.5 molar parts of reactive halogen per mol of availableamino nitrogen in the catalyst component. Depending, of course, on themolecular weight of the halogen compound and the quantity of aminocatalyst in the formulation, the halogen compound may comprise 0.1 to 3parts by weight per hundred parts of the polyol (php). The amount ofpolyisocyanate will of course vary with the particular polyisocyanateemployed and the particular polyol(s) present but in general will be inthe range of about 50 to 300 php. While tertiary amine catalyst may beemployed alone, it is preferred to include a small amount of tinco-catalyst therewith, from as little as 0.02 and up to about 0.2 partsper hundred of polyol. In blown RIM products the preferred blowing agentis a fluorocarbon and generally will constitute up to about 4 pph. Noblowing agent is ordinarily employed for molded solid products. Theformulations ordinarily include a chain extender, such as a short chaindiol in the range of 10 to 50 php.

EXAMPLES 2-10

Formulations 3A or 3B of Table 3 were used to prepare RIM products inwhich the halogen compound, e.g. CEF, was increased from zero to wellbeyond the upper limit permitted to assure maintenance of optimumphysical properties. The physical properties for each of the resultingRIM products are set forth in Table 4 below.

                  TABLE 3                                                         ______________________________________                                                         A       B                                                    ______________________________________                                        Pluracol 380       86.3     100                                               1,4-butanediol     23.0     22.1                                              Fluorocarbon       1.7      3.5                                               Catalyst                                                                      Triethylenediamine 0.5-1.0  0.5                                               Tin, Dibutyl Tin diLaureate                                                                      0.04     0.02                                              CEF                As shown in Table 4                                        Mondur CD          80.5     79.5                                              ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________    EXAMPLE          2    3    4    5    6     7    8    9    10                  __________________________________________________________________________    FORMULATION      3A   3A   3A   3A   3A    3A   3B   3B   3B                  TEDA             1.0  1.0  1.0  1.0  0.75  0.5  0.5  0.5  0.5                 CEF              0.0  1.5  1.0  0.5  1.5   1.5  0.0  2.5  5.0                 DENSITY, LBS./CU. FT.                                                                          60.1 59.5 55.4 55.0 58.1  58.8 67.0 63.8 63.0                SHORE D HARDNESS 49.5 48.0 54.0 52.0 48    52.0 49.0 46.0 43.0                TEAR, LBS. - FORCE                                                                             --   --   --   --   --    --   272  226.3                                                                              200.3               TEAR, LBS. - % ELONGATION                                                                      100  103.6                                                                              104.5                                                                              102.8                                                                              111.0 113.2                                                                              153  68   73                  100% MODULUS     2292 2090 2080 2206 2106  2083 2000 1088 1060                TENSILE, PSI     2332 2272 2310 2303 2351  2367 2253 1046 1018                FLEXURAL MODULUS                                                               -20° F.  47.5 52.0 67.0 56.3 64.7  65.0 46.0 45.0 41.8                  72° F.  23.0 24.0 35.7 30.0 29.3  33.7 20.0 19.2 17.2                  158° F. 9.5  9.0  18.7 12.0 12.8  14.8 8.2  9.0  8.0                 MODULUS RATIO                                                                  -20°/158°                                                                       5.0  5.8  3.4  4.7  5.1   4.4  5.6  5.0  5.2                 __________________________________________________________________________

From the data set forth in Table 4, it is clear that as the CEF levelsin the formulation were increased to 2.5 php and above, the shore Dhardness, tear strength, elongation, modulus, tensile and flexuralmodulus strengths were all markedly reduced. Therefore, it has beenestablished that as the CEF level is increased to approach levelsnecessary to impart significant flame retardant properties, the RIMproducts have significantly inferior physical properties from theproducts obtained from the method of the present invention.

What is claimed is:
 1. An elastomeric composition for the production ofRIM polyurethane products comprising per hundred parts of polyetherpolyol therein:10 to 50 parts of a diol chain extender; 50 to 300 partspolyisocyanate; 0 to 4 parts of volatile fluorocarbon blowing agent, 0.1to 1.0 parts of tertiary amine catalyst; and 0 to 0.2 parts of organotin catalyst; together with 0.1 to 3 parts of a reactive organic halogencompound.
 2. An elastomeric composition as defined in claim 1 whereinsaid tertiary amine catalyst is a ditertiary amine.
 3. An elastomericcomposition as defined in claim 1 wherein said tertiary amine istriethylenediamine.
 4. An elastomeric composition as defined in claim 1containing 0.1 to 1.0 parts of triethylenediamine and 0.01 to 0.04 partsof organo-tin catalyst.
 5. An elastomeric composition as defined inclaim 1 or 3 wherein said organic halogen compound is a chlorophosphate.6. An elastomeric composition as defined in claim 1 or 3 wherein saidorganic halogen compound is tris(chloroethyl)phosphate.